1. Field of the Invention
The present invention pertains to downhole tools typically used in the oil and related industries for providing an annular seal and/or anchoring system between one conduit disposed in another and, in particular, the present invention is directed to an arrangement for adjusting the slack in the anchoring mechanism for such tools.
2. Background Art
There a number of different downhole tools used in the well drilling industry which provide for a seal to be established in the annulus between one conduit and another in the well such as between the well bore and tubing, or between the well casing and tubing disposed within the casing. A typical example of the class of tools described herein is known in the trade as a packer and is characterized by an elongated cylindrical inner housing or mandrel around which are disposed one or more resilient collars which may be axially compressed to expand radially outward into sealing engagement with the inner wall of a conduit to form an annular seal. Typically, downhole tools such as packers also include anchoring mechanisms known as slips comprising radially extendable toothed gripper elements which are engageable with the conduit inner wall for anchoring the tool in the desired position so that the seal elements are not required to withstand substantial axial loading. The seal elements and slip mechanism are usually arranged axially in an assembly which includes a setting mechanism disposed on and around the aforementioned mandrel.
Some downhole tools such as retrievable packers are fairly complex mechanical devices and require a number of components making up the setting mechanism, the slip assembly and the packing element assembly. The manufacturing tolerances required for maintaining resonable production costs, as well as the inherent design characteristics of, for example, the slip assembly results in considerable slack or axial looseness of the components when the tool is assembled in the relaxed or "running" condition. In particular, the accepted and preferred design for the slip assembly results in considerable axial looseness of the coacting parts when the slip assembly is in the relaxed or retracted position. A preferred arrangement of the slip assembly comprises radially movable slip elements having gripper teeth on the exterior surface thereof, which elements are cooperable with so called cone or wedge members. The slip cones or wedge members are adapted to be moved axially on the exterior of the mandrel to force the slip elements radially outwardly into gripping engagement with the conduit inner wall surface. The slip elements and the wedge members are normally provided with cooperating tenon and groove portions of a T-slot or dovetail configuration to retain the members in assembly with each other and to provide for the relative movement necessary during the setting and retracting operations.
The relatively loose fit between coacting parts inherent in the design of elements as described above and necessary for proper mechanical operation results in the possibility of the slip elements being so loose during the running operation of the tool that they may accidentally come into contact with the interior wall of the well conduit, which contact may result in damage to the slip elements as well as other tool components. Hence, it is desirable that in the relaxed condition of the sealing elements and the slip mechanism that there be no slack in the assembly which will permit outward radial movement of the slip elements which could result in damage to these elements or unwanted snagging to the tool during the running and retrieving operations. The present invention solves the problem of providing a slack adjustment mechanism for downhole well tools employing radially movable anchoring slips or the like, which mechanism is simple, reliable and is disposed on the tool in a highly preferred location.
Moreover, the types of tools in which the present invention is embodied tend to be mechanically complex, expensive to manufacture and available in many different models for different specific purposes thereby requiring manufacturers and users to maintain a large number of different parts for the substantial number of different tool models. However, the present invention provides a mechanically simple slack adjusting feature which is located in a highly preferred position on the tool and in which position the associated tool parts are usually not required to be of a different configuration, for different tool models.